05000260/LER-2019-002, Main Steam Relief Valves Lift Settings Outside of Technical Specifications Required Setpoints
| ML19199A333 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 07/18/2019 |
| From: | Hughes D Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2019-002-00 | |
| Download: ML19199A333 (9) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 2602019002R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 July 18, 2019 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Subject:
Browns Ferry Nuclear Plant, Unit 2 Renewed Facility Operating License No. DPR-52 NRC Docket No. 50-260 Licensee Event Report 50-260/2019-002-00 10 CFR 50.73 The enclosed Licensee Event Report provides details of the inoperability of Main Steam Relief Valves for longer than allowed by plant Technical Specifications. The Tennessee Valley Authority is submitting this report in accordance with Title 10 of the Code of Federal Regulations 50.73(a)(2)(i)(B), as any operation or condition which was prohibited by the plant's Technical Specifications.
There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact J. L. Paul, Site Licensing Manager, at (256) 729-7874.
Re~tQ D. L. Hughes Site Vice President Enclosure: Licensee Event Report 50-260/2019-002 Main Steam Relief Valves Lift Settings Outside of Technical Specifications Required Setpoints cc (w/ Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant NRC Project Manager - Browns Ferry Nuclear Plant
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. Page Browns Ferrv Nuclear Plant Unit 2 05000260 1 OF 8
- 4. Title Main Steam Relief Valves Lift Settings Outside of Technical Specifications Required Setpoints
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved I
Sequential I Rev Facility Name Docket Number Month Day Year Year Month Day Year N/A N/A Number No.
05 29 2019 2019 002 00 07 18 2019 Facility Name Docket Number N/A N/A
- 9. Operating Mode 11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 0 20.2201 (b)
D 20.2203(a)(3)(i) 0 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 0 20.2201 (d)
D 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(B)
- 50. 73(a)(2)(viii)(B)
D 20.2203(a)(1 )
D 20.2203(a)(4)
D 50.73(a)(2)(iii)
- 50. 73(a)(2)(ix)(A)
D 20.2203(a)(2)(i) 0 50.36(c)(1)(i)(A)
D 50.73(a)(2)(iv)(A)
- 50. 73(a)(2)(x)
- 10. Power Level D 20.2203(a)(2)(ii) 0 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71(a)(5)
D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 091 D 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
~ 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii) 0 50.73(a)(2)(i)(C) 0 OTHER Specify in Abstract below or in
C. Dates and approximate times of occurrences
Dates March 29, 2017 April 27, 2018 May 7, 2018 May 10, 2019 March 2, 2019 May 29, 2019 Occurrence Unit 2 entered Mode 2 at beginning of cycle 20 (U2C20)
BFN-2-PCV-001 -0041 declared inoperable due to excessive leakage Unit 2 entered Mode 4 for the replacement of BFN-2-PCV-001 -0041 Unit 2 entered Mode 2 following the replacement of BFN-2-PCV-001 -0041 Unit 2 entered Mode 4 for U2R20 NWS Technologies notified the TVA with as-found testing results of the thirteen Unit 2 MSRV pilot valves removed during U2R20
D. Manufacturer and model number of each component that failed during the event
The failed components were all Target Rock Corporation two-stage pressure control valves, model number 7567F.
E. Other systems or secondary functions affected
No other systems or secondary functions were affected by this event.
F.
Method of discovery of each component or system failure or procedural error
Failure of MSRVs BFN-2-PCV-001-0004, BFN-2-PCV-001 -0018, and BFN-2-PCV-001-0019 was discovered at NWS Technologies during their as-found testing of the thirteen MSRV two-stage pilot valves which were removed during U2R20. Failure of MSRV BFN-2-PCV-001-0041 was discovered based upon leakage estimates during plant operation and subsequent testing by NWS Technologies.
G. The failure mode, mechanism, and effect of each failed component
MSRVs BFN-2-PCV-001 -0004, BFN-2-PCV-001-0018, and BFN-2-PCV-001-0019 failed due to corrosion bonding to the valve seats as a result of the platinum anti-corrosion coatings flaking off. Two additional test lifts on each valve were within the acceptance criteria of +/- 3 percent of the required setpoint, indicating corrosion bonding caused each pilot valve to initially lift high.
REV NO.
00 2019 -
002 Failure of MSRV BFN-2-PCV-001-0041 was caused by a delamination of a portion of the platinum anti-corrosion coating which lead to the leak.
H. Operator actions
There were no operator actions associated with this event.
I.
Automatically and manually initiated safety system responses
There were no automatic or manual safety system responses associated with this event.
Ill.
Cause of the event
A. Cause of each component or system failure or personnel error MSRVs BFN-2-PCV-001-0004, BFN-2-PCV-001 -0018, and BFN-2-PCV-001 -0019 failed above their setpoint band due to valve disc corrosion bonding to the valve seat as a result of the platinum anti-corrosion coating flaking off. In the case of MSRV BFN-2-PCV-001-0041, the loss of the platinum anti-corrosion coating led to leakage which affected its lift setpoint.
No human performance related root causes were identified.
IV.
Analysis of the event
BFN Unit 2 TS Limiting Condition for Operation (LCO) 3.4.3 requires twelve Operable S/RVs during Modes 1, 2, and 3. If one or more required S/RVs become inoperable, Required Action A. 1 requires entering Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and Required Action A.2 requires entering Mode 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. S/RV Operability requires that S/RVs be within a +/- 3 percent band of their setpoint values in accordance with Surveillance Requirement (SR) 3.4.3.1. BFN Unit 2 has thirteen MSRVs to satisfy this requirement with margin.
When tested, the following four S/RVs were outside the allowable+/- 3 percent band.
S/RV Number Set~oint Test Result Difference BFN-2-PCV-001-0004 1155 1215
+5.2%
BFN-2-PCV-001 -0018 1145 1197
+4.5%
BFN-2-PCV-001-0019 1135 1214
+7.0%
BFN-2-PCV-001-0041 1155 1230
+6.5%
00 Prior to startup from U2R20, all thirteen MSRV pilot valves were replaced with refurbished valves which were certified to lift within +/- 1 percent of their setpoint. Operating Experience has shown that Target Rock two-stage MSRV setpoint drift is not a uniform, linear process. The corrosion bonding increases at a random rate. Without an accurate and reliable model for predicting or estimating the setpoint drift development, the point in time where the setpoint exceeded the +/- 3 percent limit cannot be reliably determined. Since this drift occurred during the operating cycle when the MSRVs were installed, MSRVs BFN-2-PCV-001-0004, BFN-2-PCV-001 -0018, and BFN-2-PCV-001-0019 are conservatively considered to be inoperable for an indeterminate period of time between March 29, 2017, and March 2, 2019. MSRV BFN-2-PCV-001 -0041 was considered to be inoperable from April 27, 2018 until entering Mode 4 on May 7, 2018, for replacement. More than one MSRV was considered to be inoperable during the entire operating cycle and longer than permitted by TS 3.4.3.
TS LCO 3.0.4 states that when an LCO is not met, entry into a Mode or other specified condition in the Applicability shall only be made when the associated ACTIONS to be entered permit continued operation in the MODE or other specified condition in the Applicability for an unlimited period of time. Because Unit 2 made Mode changes from a mid-cycle on May 10, 2018, while TS 3.4.3 was not met, Unit 2 was in violation of TS 3.0.4.
V.
Assessment of Safety Consequences
System availability was not impacted by this event. The failure of the MSRV pilot valves to meet their TS 3.4.3 specified mechanical setpoints does not impact their remote-manual operation or activation through the MSRV Automatic Actuation Logic, since these operating modes and functions rely upon electrically signaled control air solenoids to open the MSRV pilot valves.
The bounding maximum over-pressurization analyses are performed each fuel cycle to show that the requirements of the ASME code regarding overpressure protection are met. The analyses are performed specifically to show that the dome pressure TS limit of 1325 psig is not exceeded and that the vessel pressure does not exceed the limit of 1375 psig. In addition, the Anticipated Transient Without Scram (A TWS) pressurization analyses are also performed to demonstrate that the 1500 psig peak vessel pressure limit is not exceeded.
For the ASME analysis, the existing analysis setpoint groupings conservatively bound the eleven lowest as-found MSRV opening setpoints; however, the highest as-found valve opening setpoint falls outside the bounds of the existing analysis valve groupings. Therefore, the limiting ASME overpressurization event, identified as the ASME with main steam isolation valve closure at 102 percent rated power/ 105 percent rated flow at coastdown, was re-analyzed based on the as-found lift settings. The re-analysis determined a maximum dome pressure of 1272 psig and maximum vessel pressure of 1305 psig, which are within the ASME limits.
For the A TWS analysis, the existing analysis valve setpoint groupings conservatively bound the eight lowest as-found MSRV opening setpoints; however, the four highest valve setpoints fall 00 YEAR 2019
- 3. LER NUMBER SEQUENTIAL NUMBER 002 outside the existing analysis valve groupings. Therefore, the limiting A TWS overpressurization event, identified as the A TWS pressure regulator failed open at 100 percent rated power I 81 percent rated flow at beginning of cycle, was re-analyzed based on the as-found lift settings. The re-analysis determined a maximum vessel pressure of 1414 psig, which is within the ATWS limit.
TS Bases 3.4.3 states that the overpressure protection system must accommodate the most severe pressurization transient. The MSRVs remained capable of maintaining the reactor pressure below 1375 psig, which is the ASME code limit (110 percent of the vessel design pressure). The valves remained capable of performing their required safety function. Therefore, as defined in NEI 99-02, failure of the MSRV pilot valves was not a safety system functional failure.
Based on the above, the TVA has concluded that sufficient systems were available to provide the required safety functions needed to protect the health and safety of the public.
REV NO.
00 A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event Each BFN operating unit has a non-safety related, electrical logic system (MSRV Actuation Logic) installed, which provides defense-in-depth against MSRV setpoint drift by electrically opening MSRV groups based upon setpoints at 1135 psig, 1145 psig, and 11 55 psig.
Therefore, during a reactor pressure transient event, the four 1135 psig group MSRVs, followed by the four 1145 psig group MSRVs, and finally the five 1155 psig group MSRVs would receive an electrical open signal, providing a defense-in-depth function to allow the valves to perform their safety function.
B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident This event did not occur when the reactor was shutdown.
C. For failure that rendered a train of a safety system inoperable, estimate of the elapsed time from discovery of the failure until the train was returned to service TS 3.4.3 require twelve of the thirteen S/RVs to be operable for S/RV system operability. It is conservatively considered that less than twelve S/RVs were operable for the duration of U2C20 from March 29, 2017, to March 2, 2019.
VI.
Corrective Actions
Corrective Actions are being managed by the TVA's corrective action program under Condition Reports(CRs) 1286467, 1410577, 1521190.
A. Immediate Corrective Actions
All thirteen of the BFN Unit 2 MSRV pilot valves were replaced with refurbished valves during U2R20. As-left testing verified that these refurbished pilot valves were within +/- 1 percent of their setpoints.
B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future As most recently discussed in LER 50-259/2018-007-00, a flaking issue has been noted with the platinum coated pilot discs. Corrective actions from that LER included revising the inspection, repair, and reassembly procedure to add nitrogen leak testing of the pilot valves prior to platinum coating. This procedure requirement was added in 2017, and the valves installed during the U2R 19 refueling outage did not have this step of nitrogen leak testing prior to platinum coating within the scope of their rebuilds. Nitrogen leak testing of the pilot valves prior to platinum coating continues to be the corrective action to prevent recurrence.
In addition, since the coating issues that occurred in Spring 2017, BFN has utilized a 1 or 2 disc holder during the coating process to reduce the "shadowing" effect on the discs that can occur when using the 3 disc holder. Also, the Boiling Water Reactor Owners' Group (BWROG) is currently working toward a solution to improve the quality and adhesion of the platinum coating on the discs. These improvements include changing the method of applying the platinum to the pilot discs from Ion Beam Assisted Deposition (IBAD) to Plasma Enhanced Magnetron Sputtering Deposition (PEMS), which data shows provides a more consistent and forgiving finish on the pilot valve seating surface and gives the platinum more inherent ductility. Two of the thirteen pilots installed during U2R20 have discs with platinum applied with the PEMS method. The PEMS method will now be used for all pilot discs.
00
VII. Previous Similar Events at the Same Site
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, the NRG may not conduct or sponsor, and a person is not required to respond ID, the information collection.
YEAR 2019
- 3. LER NUMBER SEQUENTIAL NUMBER 002 REV NO.
00 A search of BFN Units 1, 2, and 3 LERs for the last five years identified six LE Rs associated with MSRV lift settings outside of TS required setpoints.
LER 50-259/2018-007-00 Unit 1 Cycle 12 LER 50-296/2018-004-00 Unit 3 Cycle 18 LER 50-260/2017-004-00 Unit 2 Cycle 19 LER 50-259/2016-005-00 Unit 1 Cycle 11 LER 50-296/2016-004-00 Unit 3 Cycle 17 LER 50-259/2014-006-00 Unit 1 Cycle 10
VIII. Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments. Page _8_ of _8_